Recent advances and future challenges in the explanation and exploitation of the network glass transition of high sugar/biopolymer mixtures

Through the years, the concept of glassy phenomena evolved from non-science to a highly specialized subject following the appreciation that structural properties or product defects could be rationalized on the basis of this amorphous vitreous transition. Special reference will be made in this review to sugar glasses in the presence of biopolymers which, increasingly, are used to innovate (e.g., replace gelatin) in confections, ice cream, boiled down sweets, etc. Keeping in mind that the subject cuts across several conventional fields, this manuscript is written with several objectives in view. I deemed it necessary to provide a historic itinerary of the nature of the rubber-to-glass transition in association with the concepts of plasticizing and unfreezable water. That should facilitate comprehension and hopefully encourage young scientists to take an interest in the field that continues to offer considerable challenges, as well as opportunities. Second, the food scientist is exposed to the sophisticated synthetic polymer approach pioneered by J.D. Ferry and his colleagues via the WLF equation/free volume theoretical framework. Extension of this school of thought to biomaterials introduces the concept of mechanical or network glass transition temperature, which is contrasted to data obtained using differential scanning calorimetry. Applications of the network T, as a relevant indicator for evaluating the stability criteria and the quality-control aspects of foodstuffs are also discussed. All along, information available in the literature is critically presented ranging from the misuse of the WLF equation to a recent challenge to the theory mounted by the coupling model, which addresses in some detail the physics of interactions and the cooperativity of molecular mobility at the vicinity of T-g.